In terms of, "how cheap can you make your first 5 gallons of beer?", I would do something like this.
Sanitize fermenter. Follow the instructions of beer mix, put in fermenter. Fermentation should take 2 to 5 days. Leave in fermenter for 7 to 10 days (this will help to clarify).
Sanitize hoses, pots, and bottles with 1 tsp. of bleach to 1 gal of water, rinse everything 2 times with fresh water. Siphon wort (unfermented beer) out of fermenter into pots and pans. Clean out sludge and siphon wort back to fermenter. Heat 1 qt of the beer and add 3/4 cup of sugar and boil 1 min. Add this back to the 5 gal.
Siphon into bottles. I put the hose to the bottom of the bottles and when it reaches the lip I stop the flow and remove the hose. This leaves enough space for the carbonation process. Wait 4 weeks before drinking.
In about 5 weeks and $29 you have home brew. Generally don't think of this as a cheep way to have beer but a hobby you can enjoy the fruits of. I have had a lot of equipment given to me by ex-brew people but still have about $100 invested in equipment.
Note: I have used the soda bottles about 4 times and I don't know the limit of the reuse.